1. Field of the Invention
The present invention relates to clathrates of certain aromatic hydrocarbons and complex aluminum salts. More particularly, the present invention relates to liquid clathrates of aromatic hydrocarbons and complex aluminum salts which contain at least one multidentate macrocyclic compound complexed with the cationic portion of the complex salt.
2. Description of the Prior Art
Liquid clathrates of small ring aromatic compounds and complex metal salts formed by the reaction of simple alkali metal or ammonium salts with trimethylaluminum in a mole ratio of 1:2 are known as described in a series of publications authored by J. L. Atwood et al, in the Journal of Organometallic Chemistry (Vol. 66, pp. 15-21 (1974); Vol. 42, pp. C77-79 (1972); Vol. 61, pp. 43-48 (1973); and Vol. 65, pp. 145-154 (1974). The complex metal salts which form the liquid clathrates with certain aromatic solvents are prepared by reacting simple salts such as the alkali metal or ammonium halides, azides, thiocyanates and selenocyanates with trimethylaluminum in appropriate amounts such that salts of the stoichiometry, M[Al.sub.2 (CH.sub.3).sub.6 X] are formed. When the complex metal salts are treated with certain aromatic compounds such as benzene or toluene, liquid complexes or clathrates form which contain at least two and up to about 13 aromatic molecules per complex salt molecule. The liquid clathrates can be distinguished from the rest of the particular aromatic hydrocarbon solvent to which the complex metal salt is exposed by the formation of a second liquid layer which is immiscible with the hydrocarbon solvent.
Liquid clathrates are also known as described in U.S. Pat. No. 4,024,170 which are formed by the complexation of 1.5 to 30 moles of an aromatic hydrocarbon compound and a complex aluminum nitrate salt of the formula M {Al.sub.2 [(CH.sub.2).sub.x CH.sub.3).sub.6 NO.sub.3 } wherein x is an integer of 1 to 3 and M is an alkali metal cation, ammonium ion, or the like. It is believed that the clathrate forming ability of the aluminum containing salts is attributable to the angular characteristics of the nitratecontaining anion portion of the salt.
U.S. Pat. No. 3,280,025 shows a method of extracting aromatic hydrocarbons from liquid hydrocarbon material by contacting the liquid hydrocarbon material with a complex of a trialkylaluminum and a salt having the formula R.sub.n MX, wherein R is alkyl, usually of 2 to 5 carbon atoms, M is one of the elements: nitrogen, arsenic, phosphorous, sulfur, selenium or tellurium, X is a halogen and n is 3 or 4 depending upon the element M. The trialkylaluminum compound and R.sub.n MX compound react to form a complex which selectively forms a clathrate with aromatic hydrocarbons in a liquid hydrocarbon.
While the prior art complex salts all form liquid clathrates with aromatic hydrocarbons, the types of complexes which form clathrates are limited, and the extent of clathrate formation is also limited. A need, therefore, continues to exist for a greater array of complex salts which form clathrates of specific compositions involving a large number of aromatic hydrocarbon molecules per complex salt molecule thereby providing a broader spectrum of choices for a given separation process.